1. Field of the Invention
The present invention relates to an ultrasonic transmitting and receiving apparatus for observing the organs etc. within a living body by transmitting and receiving the ultrasonic waves.
2. Description of a Related Art
Conventionally, in order to acquire a three-dimensional image by transmitting and receiving the ultrasonic waves, using a one-dimensional transducer array with a position sensor, a three-dimensional image is created by electrically steering the transmitted and received ultrasonic waves so as to acquire a two-dimensional images with respect to a section in a depth direction, and further, synthesizing the two-dimensional images acquired by mechanically moving the one-dimensional transducer array. However, according to the technique, since there is a time lag in the mechanical movement of the one-dimensional transducer array, the two-dimensional images at different times are synthesized, so that the synthesized image becomes blurred. Therefore, the technique is unsuitable for imaging of an object with a movement such as a living body.
In order to solve such a defect, it is more advantageous to acquire a three-dimensional image using a two-dimensional transducer array. Richard E. Davidsen et al., “TWO-DIMENSIONAL RANDOM ARRAYS FOR REAL TIME VOLUMETRIC IMAGING”, ULTRASONIC IMAGING, Vol. 16 (U.S.), Academic Press, 1994, pp. 143-163 discloses the multibeam reception using a two-dimensional transducer array for transmitting the ultrasonic beams to one region and simultaneously receiving the ultrasonic echoes reflected from 16 directions within the region and processing them. Further, U.S. Pat. No. 6,179,780 discloses the multibeam transmission for simultaneously transmitting the ultrasonic beams to a plurality of regions.
Furthermore, JP-A-8-38473 discloses an ultrasonic diagnosing apparatus capable of simultaneously generating the ultrasonic transmission beams having different frequency bands, focal ranges and orientations by generating the transmission signals having different frequency bands for one transmission. However, since the maximum amplitude of the transmission signal increases by synthesizing the frequency signals, it is necessary to increase the withstand voltage of the ultrasonic transducer, and it is also necessary to increase the maximum output voltage of the transmission signal generating circuit, and thereby, the power consumption also increases.
On the other hand, JP-B-3356996 discloses an ultrasonic diagnosing apparatus for simultaneously forming the transmission beams without the need of any special driver or the like. In the ultrasonic diagnosing apparatus, in order to form the transmission beams by one transmission, a plurality of vibrating elements are divided into a plurality of transmission groups, and the transmitting circuits for supplying a plurality of transmission signals having different transmission frequencies with respect to the respective transmission group are included.
Similarly, JP-B-3255815 discloses an underwater sonar equipment having an ultrasonic wave transmitter/receiver in which the circular vibrating surfaces can be separately arranged, but not occupying a large area. In this underwater sonar equipment, the transmitter/receiver is formed by arranging the ultrasonic vibrators so that all of their vibrating surfaces may be located within the first circle along the horizontal surface. A desired beam can be formed while keeping the occupied area of the vibrating surfaces of the ultrasonic vibrators small by grouping these ultrasonic vibrators into the first to sixth ultrasonic vibrator groups with the second to fifth circles inscribed in the first circle and having the same diameter smaller than the first circle, and driving these ultrasonic vibrator groups appropriately and selectively.
However, as disclosed in JP-B-3356996 and JP-B-3255815, when the multibeam transmission is performed in a state in which the vibrators are divided into the groups, there is a problem that the intensity of each transmission beam becomes lower.